Liquid crystal electro-optical device

ABSTRACT

A brighter active matrix type liquid crystal electro-optical device with a higher contrast, yet having a wider visual angle is realized, said liquid crystal electro-optical device comprises a liquid crystal layer and means for applying an electric field to the liquid crystal layer in the direction parallel to the substrate, wherein the liquid crystal layer comprises a liquid crystal material dispersed in a polymer material. Also a liquid crystal electro-optical device comprising a liquid crystal layer disposed on a substrate is included, wherein the transmission mode or the dispersion mode of an incident light is selected by an electric field applied to the liquid crystal layer in the direction parallel to the liquid crystal layer.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a liquid crystal electro-opticaldevice having excellent electric properties and contrast, and which iscapable of realizing a bright and uniform display over the entire imageplane.

[0002] According to the basic principle for the operation and thedisplay of a liquid crystal electro-optical device, in general, a liquidcrystal electro-optical device has such a constitution that an organicmaterial, more specifically, a liquid crystal material, is interposedbetween a pair of substrates, and the light passing through the liquidcrystal material is modulated by changing the intensity of the electricfield which is generated by the electrode formed between the pair ofsubstrates. As a result of the modulation, the change is recognized asthe change in the quantity of light.

[0003] Accordingly, if a specified electric signal is supplied to theelectrode, the electric signal can be displayed as a visually observablestate. Thus, a desired image can be formed by combining a plurality ofelectrodes and by then applying an electric signal corresponding to theimage data.

[0004] The optical modulation in a conventional liquid crystalelectro-optical device is realized by applying the electric fieldperpendicular to the substrate, and then changing the intensity of theelectric field to thereby change the alignment direction of the rod-likeliquid crystal molecules in the direction parallel to the substrate orin the direction perpendicular to the substrate. In this case, ingeneral, a polarizer sheet must be incorporated into the device toobtain a linearly polarized light from the incident light, because thelight is modified by using the optical anisotropy of the liquid crystalmaterial, i.e., one of the characteristics of a liquid crystal material.

[0005] However, in case of a liquid crystal electro-optical device basedon the operation principle above, although a normal display state isrealized when the display plane is viewed from the directionperpendicular thereto, the display becomes dark and unclear when thedisplay plane is viewed from a direction oblique thereto; in case of acolor display, moreover, a decoloring phenomenon occurs.

[0006] By considering the relation between the output light from theliquid crystal electro-optical device and the alignment direction ofliquid crystal molecules, the phenomenon above can be explained asfollows.

[0007] In case of employing a constitution as such that the liquidcrystal molecules are aligned in a direction perpendicular to thesubstrate, the molecules are aligned in a direction as such that themajor axes thereof are arranged in parallel to each other in displayingan image, but the observed light is a light from the perpendicular planeof randomly positioned liquid crystal molecules.

[0008] On comparing the case of viewing the display from the directionperpendicular to the substrate and the case of viewing it from adirection slightly deviated from the direction perpendicular to thesubstrate in the constitution above, the display as viewed from thelatter view point signifies that the display is viewed from a viewpointslightly tilted with respect to the major axes of the liquid crystalmolecules. This indicates that the observation area of the output lightgreatly differs depending on the direction of viewing the display plane.

[0009] Accordingly, the degree of degradation of visual fieldcharacteristics of an observer increases with increasing deviation fromthe direction perpendicular to the display plane.

[0010] Furthermore, there is another problem in case of a liquid crystalelectro-optical device above. That is, the liquid crystal material isaligned in a specified direction by generally applying a certainalignment treatment to the substrate. However, because a strongalignment force functions in the vicinity of the substrate, the liquidcrystal molecules in the vicinity of the substrate maintain the alignedstate even when an electric field is applied thereto, or, the change inthe aligned state appears far smaller as compared with the liquidcrystal molecules positioned in the central portion of the device.Accordingly, the light is scattered in the vicinity of the substrate asto influence the display.

[0011] As means for solving the problem above, there is proposed tochange the optical characteristics by an operation mode differing fromthat of a conventional liquid crystal electro-optical device; i.e., theliquid crystal molecules are rotated only in a direction parallel to thesubstrate. The details are disclosed in JP-B-Sho 63-21907 (the term“JP-B-” as referred herein signifies “an examined published Japanesepatent application”). This operation mode is referred herein to as “IPSmode”.

[0012] A liquid crystal electro-optical device operated by IPS mode ischaracterized in that the opposing electrode for driving the liquidcrystal material, which is provided to the opposing substrate side isdisposed on the substrate side on which the pixel electrode is provided.That is, a pixel electrode and an opposing electrode are provided on oneof the pair of substrates that are provided faced to each other.

[0013] Thus, an electric field is formed between the pair of electrodesformed on a single substrate. The electric field comprises the principalcomponent thereof in the direction parallel to the substrate and theliquid crystal layer. The liquid crystal molecules are thus rotatedinside a plane parallel to the substrate by this electric field.Accordingly, the liquid crystal material, which is an optically uniaxialmedium, changes the optical axis by the applied electric field, and thestate of light transmitted through the liquid crystal layer is changedby the birefringence effect as to make a display possible.

[0014] Thus, as described above, the liquid crystal molecules are neveraligned perpendicular to the substrate during the operation under anoperation in IPS mode. Accordingly, the problem of visual angleattributed to the perpendicular alignment of the liquid crystalmolecules in the operation process can be solved.

[0015] In the operation under IPS mode, a switching element such as athin film transistor is connected to the pixel electrode to realizeactive matrix drive.

[0016] However, a first disadvantage of this constitution (operation inIPS mode) is the liquid crystal alignment in the dark display state,i.e., the OFF state of electric field. In general, it is preferred thatthe liquid crystal is uniformly arranged over the entire substrate inthe state of turning OFF the electric field.

[0017] In practice, however, alignment defects form depending on thestate of rubbing, and a uniform alignment over the entire substratecannot be obtained. Accordingly, a uniform black display cannot beobtained in the practical display of black color. This is a problemwhich cannot be neglected in making substrates large-sized.

[0018] A second disadvantage of the operation in IPS mode is that theintensity distribution of the electric field is non-uniform. In the caseof IPS-mode operation in which an electric field is applied in thedirection parallel to the substrate to realize a display, the electrodefor forming the electric field is provided only on one side of thesubstrates. The electric field to be applied to the liquid crystalmolecules becomes weaker with approaching the opposed substrate, i.e.increasing a distance from the substrate having thereon the electrode.

[0019] Accordingly, a uniformity on the entire display cannot beobtained due to the non-uniformity in the rise time.

[0020] A third disadvantage of the operation in IPS mode is the lowopening ratio (low aperture ratio). In the case of operation in IPSmode, the liquid crystal is controlled by the electric field formedbetween the pair of electrodes formed on the same plane. Thus, liquidcrystal present on the upper side and in the vicinity thereof cannot becontrolled. This surely lowers the aperture ratio by the areacorresponding to the electrode.

[0021] In particular, because bright and dark states in case of theoperation in IPS mode are displayed by using the polarization of light,a polarizer sheet is indispensable. The two polarizer sheets that areincorporated in the device further lower the optical transmittance.

[0022] A dispersion type liquid crystal electro-optical device is knownas another liquid crystal electro-optical device which overcomes thedisadvantage of low optical transmittance attributed to the presence ofpolarizer sheets. A dispersion type liquid crystal electro-opticaldevice is characterized in that it requires no polarizer sheets normolecular alignment.

[0023] The constitution of a dispersion type liquid crystal comprisesgranular or sponge-like nematic, cholesteric, or smectic liquid crystalsustained in a light-transmitting solid phase polymer.

[0024] A liquid crystal electro-optical device of this type can befabricated by dispersing the liquid crystal inside the polymer byencapsulating the liquid crystal, and then forming the polymer as a filmor as a thin film on a substrate. Proposed as substances for use in theencapsulation include gelatine, gum arabic, poly(vinyl alcohol), and thelike.

[0025] Examples of a film or a thin film of a polymer materialcontaining the encapsulated liquid crystal dispersed therein include thefollowing other than those described above. For instance, mentioned are:

[0026] (1) a material comprising liquid crystal material dispersed in anepoxy resin;

[0027] (2) a material utilizing phase separation of a liquid crystal anda photocurable substance; and

[0028] (3) a material comprising a three-dimensionally connected polymermaterial impregnated with liquid crystal;

[0029] In the present specification, liquid crystal electro-opticaldevices represented by those described above are referred tocollectively as “dispersion type liquid crystal electro-optical device”.

[0030] The operating principle of the above-described dispersion typeliquid crystal electro-optical device is described below. In adispersion type liquid crystal electro-optical device, the liquidcrystal is randomly oriented without being aligned to a particulardirection in case no electric field is applied thereto (state with noelectric field). In such a state, the light is scattered because therefractive index of the liquid crystal does not match with that of thepolymer surrounding the liquid crystal. Thus, the transmission of lightis obstructed as to realize a white opaque state corresponding to thedark state of the liquid crystal electro-optical device.

[0031] If an electric field is applied in the perpendicular direction atthis instance, the major axes of the liquid crystal molecules alignperpendicular to the substrate. Thus, if the refractive index in thedirection of major axes of the liquid crystal is adjusted as such thatit may match with the refractive index of the polymer resin, a statewith uniform refractive index can be realized to prevent lightscattering from occurring. In this state, light permeates the liquidcrystal layer as to realize the bright state of the liquid crystalelectro-optical device.

[0032] Thus, light can be utilized effectively in this case because theelectro-optical effect is realized without using any polarizer sheets.

[0033] However, in a practical dispersion type liquid crystalelectro-optical device, the opacity depends on the degree of lightscattering under the state of no applied electric field. Thus, there isa problem that a display with high contrast cannot be realized. Althoughthere is a problem of lightness, a liquid crystal electro-optical deviceusing a polarizer sheet still claims superiority.

[0034] Another problem in the dispersion type liquid crystalelectro-optical device is that, in the bright state, the liquid crystalmolecules align themselves in such a manner that the major axes thereofbecome perpendicular to the substrate plane. Similarly, in a dispersiontype liquid crystal electro-optical device again, the problem of visualangle as described above also remains.

[0035] As described above, a liquid crystal electro-optical deviceoperating in IPS mode is characterized in that it has a wide viewingangle. However, it has disadvantages in that it has difficulty inincreasing the opening ratio (aperture ratio), that the electric fieldis non-uniform, and that the display plane becomes dark by the use of apolarizer sheet, etc. To increase the opening ratio (aperture ratio), itis required to further introduce the technology of advanced lithographyand to improve the liquid crystal material and the like for sustainingthe image data.

[0036] In contrast to the liquid crystal electro-optical deviceoperating in IPS mode above, a dispersion type liquid crystalelectro-optical device is characterized in that it can effectivelyutilize light because it can output the incident light as it is withoutusing any polarizer sheets. However, on the other hand, as describedabove, it has difficulty in realizing an image with high contrast, and,similar to conventional liquid crystal electro-optical devices, it has adisadvantage in that it greatly depends on the visual angle.

SUMMARY OF THE INVENTION

[0037] The present invention provides a liquid crystal electro-opticaldevice in which the disadvantages of conventional liquid crystalelectro-optical devices are solved, and characterized by both thesuperiority in high visual angle properties characteristic of a liquidcrystal electro-optical device operating in IPS mode and the superiorityin effective utilization of light characteristic of a dispersion typeliquid crystal electro-optical device.

[0038] Thus, the present invention is characterized in that thearrangement of liquid crystal molecules is controlled by a transverseelectric field in a dispersion type liquid crystal electro-opticaldevice realizing the display by the transmission and the scattering oflight. In particular, a polymer material having anisotropy in refractiveindex is used as a polymer binder constituting the dispersion typeliquid crystal layer.

[0039] More specifically, the refractive index in the direction of majoraxis of the liquid crystal is matched with the refractive index of thepolymer binder in the direction of the major axes of the liquid crystalmolecules under applied electric field, and, at the same time, therefractive index in the direction perpendicular to the above directionis matched with that in the direction of the minor axes of the liquidcrystal molecules. Thus, a uniaxial polymer material differing inrefractive index is employed.

[0040] The reason why it is necessary to use a material havinganisotropy in refractive index as the polymer material is describedbelow.

[0041] In case of a conventionally known dispersion type liquid crystalelectro-optical device of a type in which the electric field is appliedin a direction perpendicular to the liquid crystal layer, the liquidcrystal molecules align themselves in such a manner that the major axesthereof become perpendicular to the substrate when an electric field isapplied thereto.

[0042] In such a state, the light incident on the liquid crystal layerpermeate as it is by matching the refractive index of the direction ofthe minor axes of the liquid crystal molecules with that of the polymerbinder (assuming that the refractive index of the polymer is isotropic).

[0043] In case the constitution according to the present invention isemployed, the liquid crystal molecules are orientated as such that thedirection along the major axes is parallel to the substrate. Thus,incident light enters into each of the liquid crystal molecules from adirection perpendicular to the major axes of the liquid crystalmolecules.

[0044] Then the uniaxial polymer binder is placed in the followingmanner. The refractive index in the direction of the major axes of theliquid crystal molecules is matched with that of the polymer binder inthe direction of the major axes of the liquid crystal molecules underapplied electric field, and, at the same time, the refractive index inthe direction perpendicular to the above direction is matched with thatin the direction of the minor axes of the liquid crystal molecules.Thus, a uniaxial polymer material differing in refractive index isemployed.

[0045] The ratio of light scattered under no applied electric field canbe increased by using a uniaxial polymer.

[0046] That is, in case the major axes of the liquid crystal moleculesare displaced from the direction perpendicular to the liquid crystallayer, the difference in refractive indices between the polymer binderin the direction of the path of incident light and the liquid crystalmolecules can be further increased. Thus, incident light can bescattered more strongly as compared to a case using a conventionalisotropic polymer resin.

[0047] Thus, the ratio of the transmission of incident light underapplied electric field to the scattering of incident light under noapplied electric field can be increased to thereby realize a displayhaving a high contrast ratio.

[0048] By employing the constitution above, a liquid crystalelectro-optical device having an improved visual angle based on thebirefringence effect and an improved contrast attributed to the increasein scattering effect under no applied electric field can be implemented,while also acquiring a bright display characteristic of a dispersiontype liquid crystal electro-optical device which requires no polarizersheets.

[0049] Usable liquid crystal materials include materials exhibitingnematic, cholesteric, or smectic properties. Particularly it ispreferred to use a nematic liquid crystal being dispersed in atransparent resin.

[0050] In the present invention, particularly selected are nematicliquid crystals having a positive or a negative dielectric anisotropy.The visual angle can be further increased by using a liquid crystalhaving small anisotropy in refractive index.

[0051] As polymer binders which sustain the liquid crystal in adispersed state, usable are the ultraviolet-curable types or thethermosetting types. Specifically, as an ultraviolet-curable resin ismentioned an urethane acrylate based resin, and mentioned as athermosetting resin is an epoxy based resin.

[0052] The mixing ratio of the liquid crystal material to the polymerbinder by weight is preferably in a range of from 5:5 to 9:1. Favorabledisplay characteristics can be obtained particularly in case the ratiois 7:3.

[0053] Further, in order to uniformly disperse the liquid crystalmaterial in the polymer material, the temperature of the mixtureobtained by mixing the liquid crystal material and the precursor of thepolymer material is once elevated to a degree at which the mixedcomponents both exhibit an isotropic state. After stirring the mixturefor a desired period of time, the temperature of the mixture is loweredto a temperature suitable for the fabrication of the device, and theresulting material is placed on the substrate by means of injectionmethod and the like.

[0054] Concerning the method for imparting anisotropy (i.e., uniaxialproperty) in refractive index in the direction perpendicular to theliquid crystal layer to the polymer material for sustaining the liquidcrystal above, there is a method comprising mechanically stretching thepolymer material. It is also possible to render the polymer anisotropicin refractive index by providing an electric field or a magnetic fieldfrom a specified direction during setting the polymer. In case of aphotocurable resin, it is possible to employ a method of providing apredetermined optical anisotropy by irradiating a light having apredetermined polarized state. These methods can be applied afterdispersing the liquid crystal and while observing the transmittedquantity of light.

[0055] The constitution of the present invention is described below.Accordingly, according to one aspect of the present invention, there isprovided a liquid crystal electro-optical device characterized in thatit comprises a liquid crystal layer and means for applying an electricfield to the liquid crystal layer in the direction parallel to thesubstrate, wherein the liquid crystal layer comprises a liquid crystalmaterial dispersed and sustained in a polymer material.

[0056] In accordance with another aspect of the present invention, thereis provided a liquid crystal electro-optical device characterized inthat it comprises a liquid crystal layer disposed on a substrate,wherein the transmission mode or the dispersion mode of an incidentlight is selected by an electric field applied to the liquid crystallayer in the direction parallel to the liquid crystal layer.

[0057] In accordance with another aspect of the present invention, thereis provided a liquid crystal electro-optical device characterized inthat it comprises a liquid crystal layer, and means for applying anelectric field to the liquid crystal layer in the direction parallel tothe substrate, wherein the liquid crystal layer comprises liquid crystalmaterial which is dispersed and sustained in the polymer materialshaving anisotropy in the refractive index.

[0058] In accordance with still another aspect of the present invention,there is provided a liquid crystal electro-optical device characterizedin that it comprises two substrates at least one of which istransparent, and a liquid crystal layer interposed between the twosubstrates, wherein the transmission mode or the dispersion mode of anincident light is selected by an electric field applied to the liquidcrystal layer in the direction parallel to the liquid crystal layer.

[0059] According to a still other aspect of the present invention, thereis provided a liquid crystal electro-optical device characterized inthat it comprises a liquid crystal layer and means for applying anelectric field to the liquid crystal layer in the direction parallel tothe substrate, wherein the liquid crystal layer comprises a polymermaterial whose refractive index in the direction of the alignment vectorunder an applied electric field corresponds to the refractive index inthe direction of the major axis of the liquid crystal molecules, andwhose refractive index in the direction perpendicular to the alignmentvector of the liquid crystal corresponds to the refractive index in thedirection of the minor axis of the liquid crystal molecules, and whereinthe liquid crystal material is dispersed and sustained in the polymermaterial.

[0060] According to a further aspect of the present invention, there isprovided a liquid crystal electro-optical device characterized in thatit comprises a liquid crystal layer and means for applying an electricfield to the liquid crystal layer in the direction parallel to thesubstrate, wherein the liquid crystal layer comprises a polymer materialwhose refractive index in the direction of the alignment vector under anapplied electric field approximately corresponds to the refractive indexin the direction of the major axis of the liquid crystal molecules, andwhose refractive index in the direction perpendicular to the alignmentvector of the liquid crystal approximately corresponds to the refractiveindex in the direction of the minor axis of the liquid crystalmolecules, and wherein the liquid crystal material is dispersed andsustained in the polymer material.

[0061] In the constitution above, as means for applying an electricfield an active matrix element is usable, and in the active matrixelements is included a thin film diode or a thin film transistor.

[0062] Usable drive methods include an active matrix method and amultiplex method.

BRIEF DESCRIPTION OF THE DRAWINGS

[0063]FIG. 1 is a schematically shown upper view of a pixel region of aliquid crystal electro-optical device according to Example 1 of thepresent invention;

[0064]FIG. 2 is a schematically shown cross section view of a pixelregion of a liquid crystal electro-optical device according to Example 1of the present invention;

[0065]FIG. 3 is a schematically shown upper view of a pixel region of aliquid crystal electro-optical device according to Example 2 of thepresent invention;

[0066] FIGS. 4(A) to 4(F) provide a diagram schematically showing crosssection view of a pixel region of a liquid crystal electro-opticaldevice according to Example 2 of the present invention;

[0067]FIG. 5 shows a scheme of a liquid crystal electro-optical deviceaccording to the present invention;

[0068]FIG. 6 shows a scheme of another liquid crystal electro-opticaldevice according to the present invention;

[0069] FIGS. 7(A) and 7(B) show the thin film transistor as viewed fromthe cross section taken along line A-A′ in FIG. 5, and are schematicallyshown cross section view of a pixel region of a liquid crystalelectro-optical device according to Examples 3 and 4 of the presentinvention;

[0070] FIGS. 8(A) and 8(B) show the thin film transistor as viewed fromthe cross section taken along line A-A′ in FIG. 5 in case the wall orthe common electrode and the drain electrode are provided in such ashape that the cross section thereof be trapezoidal, and areschematically shown cross section view of a pixel region of a liquidcrystal electro-optical device according to Examples 3 and 4 of thepresent invention;

[0071] FIGS. 9(A) to 9(E) provide an explanatory diagram showing areagradation display according to Example 5 of the present invention; and

[0072]FIG. 10 shows a block diagram of an area gradation panel accordingto Example 5 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0073] Referring to FIGS. 1 and 2, an example of a constitutionutilizing the present invention is described below. FIG. 1 is aschematic drawing showing the upper view of a part of a substrate sidecomprising formed thereon an active matrix circuit for a liquid crystalelectro-optical device of an active matrix type. FIG. 2 is aschematically shown cross section taken in line A-A′ in FIG. 1.

[0074] An example using a reverse stagger type constitution for the thinfilm transistor (TFT) is given in the constitution shown in FIGS. 1 and2.

[0075] Referring to FIGS. 1 and 2, the constitution comprises a pair ofsubstrates 101, a base silicon oxide film 102, a gate electrode 103, acommon electrode 104, a gate insulating film (silicon oxide film) 105,an island-like silicon film (a-Si film or p-Si film) 106 constituting anactive layer, a source electrode (and a source line) 107, a drainelectrode 108, and an interlayer insulating film 109. A liquid crystallayer 110 is made from a polymer material which sustains dispersedliquid crystal (113) (which comprises numerous aggregates of liquidcrystal molecules) therein.

[0076] In the constitution shown in FIGS. 1 and 2, an electric fieldparallel to the substrate (i.e., an electric field parallel to theliquid crystal layer 110) is formed between the drain electrode 108 andthe common electrode 104, and the electro-optical properties of theliquid crystal material 113 are changed by utilizing the electric field.

[0077] That is, in case no electric field is applied, each of the liquidcrystal molecules are in such a state that the major axes thereof arerandomly aligned, whereas when once an electric field is applied, all ofthe major axes of the liquid crystal molecules become aligned at oncealong one direction. Thus, the display is realized by selectingtransmission or scattering of incident light; that is, by switching thestate in which the major axes of the liquid crystal molecules arerandomly aligned to the state in which the liquid crystal molecules arealigned along a certain direction.

[0078] The refractive index of the polymer constituting the liquidcrystal layer 110 is controlled as such that the refractive index in themajor axis direction of the liquid crystal molecules (refractive indexof extraordinary light) may match with that in the direction of thealignment vector under applied electric field. Otherwise, the refractiveindices above are approximately matched. At the same time, therefractive index of the polymer binder in the same direction as that ofthe minor axis (refractive index of ordinary light) is matched, orapproximately matched, with the refractive index of the minor axisdirection of the liquid crystal molecules.

[0079] For the first and the second substrates 101, a transparentinorganic material having sufficient strength against applied externalforce, for example, glass or quartz, can be used.

[0080] An alkali-free glass or quartz glass is used as the substrate forforming thereon a TFT and the like (referred to hereinafter as “TFTsubstrate”). In case it is intended to make liquid crystalelectro-optical devices lightweight, films with small birefringence, forinstance, PES (polyethylene sulfate), can be used for the TFT substrate.

[0081] The liquid crystal material may be driven by either a multiplexmethod or an active matrix method.

[0082] In case multiplex method is employed, only two types ofelectrodes, i.e., the electrode for display and the standard electrode,need to be formed on the first substrate. In case active matrix methodis selected, other non-linear elements such as a thin film transistor(TFT) and a non-linear diode, must be additionally provided to each ofthe pixels.

[0083] As TFTs, those using a-Si (amorphous silicon) or P-Si(polycrystalline silicon) as the active layer thereof can be employed.In case the liquid crystal material is driven by active matrix method,the drive element above may be constructed by employing a knownconstitution such as of stagger type or reverse stagger type.

[0084] In case a transistor using polycrystalline silicon is employed,the peripheral drive circuit for driving the liquid crystal material canbe formed on the same plane of the substrate in which TFT is formed.

[0085] The peripheral drive circuit can be fabricated by the sameprocess as that for fabricating a TFT constituting the active matrixcircuit. The peripheral drive circuit is generally formed by acomplementary-type element comprising a combination of an n-channel typeTFT and a p-channel type TFT.

[0086] As the materials constituting each of the elements of the TFTsuch as a gate, a source, or a drain, are usable Cr, Al, ITO, and Ta.The cross section of the electrode may be either rectangular ortrapezoidal, but it is preferred that the curved plane is formed in sucha shape that the cross section thereof is a smooth plane or curvedplane. This is because the shape of the electric field that is formedinside the liquid crystal layer yields a uniform electric fieldintensity.

[0087] Silicon oxide (SiO₂) or silicon nitride (SiN) may be used foreach of the interlayer insulating film or for a TFT protective film.

[0088] For the opposed substrate 101, it is also possible to use thesame type of material as that used for the substrate on which the TFT isformed. It is not necessary to particularly form the electrode on theopposed substrate, but an electrode may be formed on either a part orthe whole of the substrate. As the electrode material, usable are themetals above and a transparent material, such as an ITO.

[0089] In order to improve the contrast, it is effective to form alight-shielding means on either the TFT substrate or the opposedsubstrate, or on both of them to shield the portion not related with thedisplay. As the light shielding means, mentioned is an examplecomprising forming a black matrix (not shown in the figure) by using apolymer material and the like containing a metal such as Cr or a blackpigment dispersed therein.

[0090] Furthermore, in case of color displays, color filters, i.e., aset of R (red), G (green), and B (blue) filters, or a set of C (cyan), M(magenta), and Y (yellow) filters, are formed on the positionscorresponding to each of the pixels. Each of the color filters may beplaced according to a stripe arrangement, delta arrangement, etc.

[0091] Because no opposed electrode is necessary for the constitutionaccording to the present invention, both the electrode and the liquidcrystal layer may be formed on a single substrate, and a transparentprotective film can be applied therein. If this constitution isemployed, the number of substrates can be reduced to one.

[0092] In the invention according to the present invention, furthermore,the electrode for applying the drive voltage to the liquid crystalmaterial is provided in a wall-like shape. More specifically, theeffective plane of the electrode forming the electric field is providedperpendicular to, or approximately perpendicular to the substrate plane.

[0093] By employing the constitution above, an electric field withuniform distribution in the direction of cell thickness can be obtained.

[0094] Thus, according to an aspect of the present invention, there isprovided a liquid crystal electro-optical device comprising at least onetransparent substrate, a liquid crystal layer comprising a polymermaterial containing a liquid crystal material dispersed therein, andmeans for applying an electric field in the direction parallel to thesubstrate, wherein at least a part of the liquid crystal material hasmajor axes aligned in a predetermined direction in parallel orapproximately in parallel with the substrate under applied electricfield, wherein the refractive index of the polymer material in apredetermined direction approximately corresponds to that of the majoraxis direction of the liquid crystal material, wherein the refractiveindex of the polymer material in a direction perpendicular to thepredetermined direction approximately corresponds to that of the minoraxis direction of the liquid crystal material, and wherein the means forapplying an electric field has an effective plane in the directionperpendicular or approximately perpendicular to the substrate.

[0095] FIGS. 5 to 8 show a specific example based on the constitutionaccording to the present invention utilizing the wall-like electrode forapplying the drive voltage to the liquid crystal material.

[0096]FIG. 5 shows a case in which an electrode having an effectiveplane on the vertical plane thereof is placed on the surface of thesupport. FIG. 6 shows a case in which the wall itself is made from anelectrode material, and an electrode having an effective plane on thevertical plane thereof is placed.

[0097]FIG. 7(A) shows the cross section taken in line A-A′ in FIG. 5.FIG. 8(A) shows a modification of the constitution shown in FIG. 7(A),in which the electrode plane is placed slightly tilted from the verticalplane.

[0098]FIG. 7(B) shows the cross section taken in line A-A′ in FIG. 6.FIG. 8(B) shows a modification of the constitution shown in FIG. 7(B),in which the electrode plane is placed slightly tilted from the verticalplane.

[0099] The example shown herein is a constitution in which a dispersiontype liquid crystal is driven by using a thin film transistor (TFT).

[0100] The constitution shown in FIGS. 5 and 6 comprises a pair ofsubstrates 400 and 401, a drain electrode 402, a common electrode 403,and a liquid crystal 404. A wall 405 is fabricated to form an electrodeof a predetermined height. Furthermore, the liquid crystal 404 isdispersed and sustained in the polymer material.

[0101] The constitution shown in FIGS. 7 and 8 comprises an entire TFTdrive portion 500, a gate line 501, a source line 502, a drain line 503,a common line 504, an interlayer insulating film 507, and an island-likesilicon film (active layer) 508. The portions shown by symbols 400 to405 are the same as those shown in FIGS. 5 and 6.

[0102] The display of the liquid crystal electro-optical devices shownin FIGS. 5 to 8 is implemented by selecting the transmission and thescattering of incident light in a manner similar to the liquid crystalelectro-optical device shown in FIGS. 1 and 2.

[0103] More specifically, when an electric field is applied, an electricfield parallel to the substrate is formed between the drain electrode402 and the common electrode 403. Thus, the liquid crystal moleculesalign themselves at the same time in the direction of the major axesthereof along the electric field. In this state, the incident lightpasses through the liquid crystal layer. On the other hand, each of theliquid crystal molecules randomly arranges the major axis thereof underno applied electric field as to scatter the incident light. A scatteringstate is realized in this manner.

[0104] The refractive index of the polymer material 406 into which theliquid crystal 404 is dispersed is matched, or approximately matched,with the refractive index in the major axis direction of the liquidcrystal molecules (refractive index of extraordinary light). At the sametime, the refractive index of the polymer material in the same directionas that of the minor axis (refractive index of ordinary light) ismatched, or approximately matched, with the refractive index of theminor axis direction of the liquid crystal molecules.

[0105] As the material constituting each of the electrodes of TFTs ofthe pixel portion and the drive circuit portion, more specifically, thedrain electrode and the common electrode, as well as the gate electrode,the gate line, etc., are usable metallic materials such as copper,aluminum, tantalum, titanium, or chromium, or a silicide material. Alsotransparent electrically conductive materials such as ITO(indium—tin—oxide), tin oxide, or indium oxide are usable.

[0106] Furthermore, the present invention is morphologicallycharacterized in that the drain electrode 402 and the common electrode403 are formed in a wall-like constitution by using an electricallyconductive material. In particular, the present invention ischaracterized in that the electrodes constituting the neighboring pixelsare disposed side by side by the back thereof.

[0107] The electrodes above may be provided in a structure as such shownin FIG. 7(B) or FIG. 8(B), so that they themselves constitute a wall.Otherwise, they may be provided in such a constitution that they areplaced on the surface of the support constituting the wall as is shownin FIG. 7(A) or FIG. 8(A).

[0108] The shape of the cross section of the wall-like electrode or thewall itself is not only limited to a rectangular one, and it may beprovided in a trapezoidal shape or a structure having a curved plane onthe edge portion thereof. In particular, by providing it in atrapezoidal shape as is shown in FIG. 8, the fabrication of thewall-like electrode can be facilitated. Moreover, the strength of thewall itself can be increased as to provide a wall resistant againstbreakage even when it is subjected to a process such as rubbing, inwhich an external force is applied. A smooth electric field can beformed by employing a shape having a curved plane on the edge portionsthereof.

[0109] Organic resins such as polyimide and acrylic resins, orinsulators such as silicon oxide, silicon nitride, or silicon oxynitrideare preferred for use as the substance which constitutes the wall 405.

[0110] In case a pixel electrode is formed by using an electricallyconductive material for the wall 405 and by providing an electrode tothe side plane or the slope plane thereof, the electrically conductivematerial must be each provided independent to each other, or aninsulating material must be provided per each pixel to insulate each ofthe pixel electrodes from each other.

[0111] If the wall-like electrode or the wall is provided with atrapezoidal cross section, the slope plane of the trapezoid ispreferably tilted at an angle of 45° or more with respect to thesubstrate plane. If the angle should be less than 45°, the area of thedrain electrode 402 or the common electrode 403 on the substrate planeincreases un-favorably as to decrease the aperture ratio.

[0112] The width of the wall-like electrode or that of the electrodeprovided on the side portion of a wall as measured at the bottom portionfrom one side plane to the other side plane (i.e., the width of thewall) is preferably 10 μm or less, and more preferably, 5 μm or less. Ifthe width should be 10 μm or more, a sufficiently high aperture ratio isunavailable.

[0113] The height with respect to the substrate of the wall-like pixelelectrode or common electrode 403, or that of a wall comprising a drainelectrode 402 or a common electrode 403 formed on the side portionthereof, i.e., the height of the drain electrode 402 or the commonelectrode 403, or the height from the bottom portion to the apex of thewall, preferably accounts for ⅛ or more of the thickness of the liquidcrystal cell. If the height of the electrode should account for ⅛ orless of the thickness of the liquid crystal cell, it becomes difficultto effectively form an electric field parallel to the substrate plane.

[0114] In the constitution according to the present invention, thecommon electrode 403 provides a predetermined common potential to eachof the pixels. Thus, a common electrode 403 may be provided at a sizecorresponding to all (or total) of the opposed pixel electrodes, or acommon electrode 403 having a size approximately the same as that of thepixel electrode 403 may be provided to each of the pixels in such amanner that it may be opposed to each of the pixel electrodes.

[0115] The drain electrode 402, the common electrode 403, or the wall405 itself may be transparent.

[0116] Reversely, a black-colored pigment may be incorporated into thematerial constituting the transparent wall, to thereby increase thelight shielding effect.

[0117] The drain line 503 shown in FIGS. 7(A) and (B) as well as inFIGS. 8(A) and (B) may be provided as a transparent electrode by usingITO and the like, or as a metallic electrode having low resistance.

[0118] It is possible to use silicon oxide or silicon nitride as each ofthe interlayer insulating materials and TFT protective films.

[0119] The distance between the electrodes is preferably in a range offrom 4 to 30 μm, and more preferably, the distance is in a range of from4 to 20 μm.

[0120] Concerning the opposed substrate 400, it is possible to use thesame type of material as that used for the substrate having a TFT formedthereon. It is not necessary to particularly form an electrode on theopposed substrate, but an electrode may be formed either partly orwholly on the surface of the substrate. In such a case, in addition tothe metals above, a transparent material, such as ITO, may be used asthe electrode material.

[0121] In order to improve the contrast, it is effective to form alight-shielding means (black matrix) on either the TFT substrate or theopposed substrate, or on both of them to shield the portion not relatedwith the display. The light shielding means, comprises a polymermaterial containing a metal such as Cr or a black pigment dispersedtherein and the like.

[0122] The pair of substrates thus fabricated above are superposed bytaking a constant interval therebetween as to provide a liquid crystalcell.

[0123] In the fabrication of a liquid crystal cell, spacers (not shownin the figure) are scattered on one of the pair of substrates tomaintain a constant distance between the substrates. If the wall has thesame thickness as that of the cell, as a matter of course, the wallitself can be used in the place of spacers.

[0124] After curing a sealing agent, a mixed material of a liquidcrystal and a polymer precursor material is placed between thesubstrates by means of vacuum injection and the like.

[0125] If difficulty is found in filling the liquid crystal cell withthe mixed material of a liquid crystal and a polymer precursor materialbecause of the presence of a wall 405, a so-called laminate method canbe employed; i.e., the material is provided dropwise on one of thesubstrates, and pressure is applied after superposing the othersubstrate.

[0126] In the constitution according to the present invention, it ispreferred to form the electrode at the same height as that of the cellthickness. In this manner, the electrode can be used in the place ofspacers. Moreover, the process step of scattering the spacers can beomitted in this case, and an electric field that is uniform in the cellthickness direction can be provided over the entire substrate.

[0127] In the constitution of the present invention, the significance ofproviding a wall or a wall-like electrode at a predetermined thicknessor higher with respect to the cell thickness is described below.

[0128] The wall, or the wall-like drain electrode 402 and commonelectrode 403 enable an electric field parallel, or approximatelyparallel, to the substrate even in the vicinity of the opposedsubstrate. Thus, an electric field with uniform intensity along the cellthickness direction can be realized.

[0129] As a result, an electric field similar to that in the vicinity ofthe substrate 401 provided thereon a drain electrode 403 and commonelectrode 403 can be applied to liquid crystal molecules located in thevicinity of the opposed substrate 400.

[0130] The present invention is described in further detail belowreferring to the preferred embodiments according to the presentinvention. It should be understood, however, that the present inventionis not to be construed as being limited to the examples below.

EXAMPLE 1

[0131] The present example describes the details of a process forfabricating a constitution according to the present invention withreference to FIGS. 1 and 2. More specifically, a case using a reversestagger type thin film transistor as TFT is described.

[0132] Firstly, a silicon oxide film from 1,000 to 3,000 Å in thicknesswas formed as a base oxide film 102 on a Corning #7059 glass substrate101 provided as an insulating substrate. The silicon oxide film can beformed, for example, by sputtering or by plasma CVD under an oxygenatmosphere.

[0133] Then, a Cr film for constituting a gate electrode 103 was formedat a thickness of from 1,000 to 5,000 Å. By patterning the Cr film, apattern as a base for the gate electrode 103 can be formed.

[0134] Then, an isotropic plasma etching was performed thereafter byusing a resist as a mask. Progressive etching was controlled and anelectrode with a curved plane was formed by appropriately setting thedischarge gas voltage. A gate electrode 103 and a common electrode 104having a curved surface were formed in this manner.

[0135] Then, a gate insulating film 105 made of silicon oxide (SiO₂) wasformed in such a manner to cover the electrodes. Alternatively, siliconnitride (SiN) can be used for the gate insulating film.

[0136] An amorphous silicon film, which is not shown in the figure, wasformed on the gate insulating film 105 by means of plasma CVD or lowpressure thermal CVD process.

[0137] Then, an active layer 106 made of amorphous silicon film wasformed by patterning the amorphous silicon film not shown in the figure.

[0138] An Al (aluminum) source electrode 107 and drain electrode 108were formed in such a manner that they may be superposed on a part ofthe active layer 106 obtained by patterning the amorphous silicon film.Curved plane was provided to the surface of each of the electrodes bymeans of isotropic plasma etching using a resist as the mask.

[0139] A silicon oxide insulating film 109 was formed as a protectivefilm of the TFT. Otherwise, a SiN film may be provided as the insulatingfilm.

[0140] A BM (black matrix) for improving contrast was formed on theopposed substrate 101 or on the TFT substrate, or on both of thesubstrates. The BM was provided to shield light of the portions notrelated with the display. The BM can be formed by using a metal such asCr, or a polymer material containing a black pigment dispersed therein.

[0141] The TFT substrate and the opposed substrate thus formed weresuperposed to form a liquid crystal panel. Spherical spacers each 3 μmin diameter were interposed between the aforementioned pair ofsubstrates to maintain a uniform distance between the two substratesover the entire panel plane.

[0142] The pair of substrates were adhered and fixed by sealing themwith an epoxy-based adhesive. The sealing was performed in such apattern that it may surround the pixel region and the peripheral drivecircuit region.

[0143] The pair of substrates thus obtained was cut into a predeterminedshape. Then, a mixture of a polymer material and a liquid crystalmaterial constituting the liquid crystal layer 110 was injected betweenthe substrates.

[0144] In the present example, a solution comprising uniformly mixedprepolymer and a nematic liquid crystal was used as the liquid crystalmaterial. More specifically, trimethylolpropane triacrylate was used asthe prepolymer in this case. The prepolymer was mixed at a concentrationof about 25% with an ordinary nematic liquid crystal material togetherwith a polymerization initiator to obtain the above solution.

[0145] Ultraviolet ray was irradiated over the entire substrate afterfilling the spacing between the substrates with the liquid crystal tocure (polymerize) the monomer formed between the substrates.

[0146] In the present case, a linearly polarized ultraviolet ray havinga predetermined polarization direction was irradiated by using apolarization filter to form a polymer having a molecular structure withorientation in a predetermined direction. In this manner, a polymerhaving anisotropy in refractive index can be obtained.

EXAMPLE 2

[0147] The present Example refers to a monolithic active matrix circuitwhose peripheral drive circuit is also formed on the substrate. Theprocess for fabricating the liquid crystal electro-optical deviceaccording to the present Example is explained below by making referenceto FIG. 3 and FIGS. 4(A) to 4(F).

[0148] Referring to FIG. 3 showing a scheme of the periphery of a pixelportion of the present Example. FIGS. 4(A) to 4 (F) show the crosssection taken along line B-B′-B″ in FIG. 3. In FIGS. 4(A) to 4(F), theleft hand side shows the process steps for fabricating the TFT of adrive circuit, whereas the right side shows the process steps forfabricating the TFT of an active matrix circuit.

[0149] Firstly, a silicon oxide film was formed as a base film on aglass substrate 301. In the present case, a silicon oxide film wasformed on a Corning #1737 glass substrate by sputtering method.

[0150] An amorphous silicon film was formed thereafter by plasma CVD orby LPCVD to a thickness of from 300 to 1,500 Å, preferably in a range offrom 500 to 1,000 Å. The amorphous silicon film thus obtained wascrystallized thereafter by annealing it at a temperature not lower than500° C., preferably, in a temperature range of from 500 to 600° C.

[0151] After the crystallization by thermal annealing, photo (laser andthe like) annealing may be effected to further increase thecrystallization.

[0152] During the crystallization by thermal annealing, a method ofadding an element such as nickel, which accelerates the crystallizationof silicon as described in JP-A-Hei 6-244103 and JP-A-Hei 6-244104 (theterm “JP-A-” as referred herein signifies “an unexamined publishedJapanese patent application”), may be used.

[0153] Then, for TFTs of a drive circuit, the silicon film was etched toform an active layer 302 (for P-channel type TFT) and 303 (for N-channeltype TFT). An active layer 304 for the TFT (pixel TFT) of a matrixcircuit was formed at the same time.

[0154] Further, a 500 to 2,000 Å thick silicon oxide film 305 was formedby sputtering under an oxygen atmosphere to obtain a gate insulatingfilm. The gate insulating film may be obtained otherwise by plasma CVD.In case of forming a silicon oxide film by plasma CVD, it is preferredto use gaseous dinitrogen monoxide (N₂O) or oxygen (O₂) and monosilane(SiH₄).

[0155] Then, an aluminum film was formed over the entire surface of thesubstrate by sputtering at a thickness of from 2,000 to 6,000 Å. Toprevent hillocks from forming during the later thermal processes,silicon, scandium, palladium, etc., was incorporated into the aluminumfilm.

[0156] Isotropic plasma etching was performed thereafter to form gateelectrodes 306, 307, 308, and a common electrode 309 (FIG. 4(A)).

[0157] The discharge gas voltage at this time was set appropriately inthis case to form a curved plane on the electrode. Then, by means of iondoping using phosphine (PH₃), phosphorus was injected to all of theisland-like active layers in a self-aligned manner by using the gateelectrode as a mask. In the ion implantation process above, the doseamount was set in a range of from 1×10¹² to 5×10¹³ atoms /cm². WeakN-type regions 310, 311, and 312 were formed as a result of this processstep (FIG. 4(B)).

[0158] A mask 313 of a photoresist which covers a part of the P-channeltype active layer and a mask 314 of a photoresist which covers a part ofthe active layer 304 for the pixel TFT were formed thereafter. The maskof a photoresist 314 was formed in such a shape that it covers to aportion 3 μm distant from the edge of the gate electrode 308.

[0159] Phosphorus was injected again by means of ion doping usingphosphine as the doping gas. The dose amount was in a range of from1×10¹⁵ to 5×10¹⁶ atoms/cm². Strong N-type regions (source and drain) 315and 316 were formed as a result.

[0160] The region 317 covered by the photoresist 314 on the pixel TFTremains as a weak N-type region because no phosphorus was injected inthe present process (FIG. 4(C)).

[0161] Next, after covering the active layers 303 and 304 of theN-channel TFT with a mask of a photoresist, boron was injected into theisland-like region 302 by means of ion doping using diborane (B₂H₆) asthe doping gas.

[0162] The dose amount was in a range of from 5×10¹⁴ to 8×10¹⁵atoms/cm². Because the dose amount of the phosphorus (see FIG. 4(C)) wassmaller than that of boron, the weak N-type region 310 formed previouslyis reversed to a strong P-type region 319.

[0163] Thus, strong N-type regions (source/drain) 315 and 316, a strongP-type region (source/drain) 319, and a weak N-type region (low densityimpurity region) 317, are formed as a result of the doping process above(FIG. 4(D)).

[0164] The drain side of the weak N-type region 317 becomes the regioncalled LDD (lightly doped drain).

[0165] Thereafter, the damage caused by doping was recovered by applyingthermal annealing at a temperature range of from 450 to 850° C. for 0.5to 3 hours. Thus, the doped impurities were activated while recoveringthe crystallinity of silicon.

[0166] Then, a silicon oxide film was formed at a thickness of from3,000 to 6,000 Å by plasma CVD over the entire surface to provide aninterlayer insulating film 320. Otherwise, this film may be a siliconnitride film or a multilayer film of silicon oxide film and siliconnitride film.

[0167] The interlayer insulating film 320 was etched by means of wetetching or dry etching to form contact holes on source/drain.

[0168] An aluminum film, or a multilayer film of titanium and aluminum,was formed at a thickness in a range of from 2,000 to 6,000 Å by meansof sputtering.

[0169] Then, patterning is performed by using a resist as a mask.Etching in this case was performed by means of isotropic plasma etching.

[0170] In this case, electrodes having curved planes were formed byproperly setting the conditions during etching. Thus are obtained theelectrodes and wirings 321, 322, and 323 for the peripheral circuit, aswell as electrodes and wirings 324 and 325 for the pixel TFT.

[0171] Further, a silicon nitride film 326 was formed as an interlayerfilm at a thickness of from 1,000 to 3,000 Å by means of plasma CVD(FIG. 4(E)).

[0172] Thus, a liquid crystal cell was fabricated by following the sameprocess steps described in Example 1. A sealing pattern as such thatsurrounds the pixel region and the peripheral drive circuit was selectedin this case.

[0173] In the present example, a resin comprising an ultraviolet-curableepoxy-modified acrylic resin containing 50% by weight of nematic liquidcrystal dispersed therein was used for the liquid crystal layer. In thefigure, liquid crystal 113 is dispersed in an epoxy-modified acrylicresin provided as the polymer.

[0174] The epoxy-modified acrylic resin in this case was cured byirradiating an ultraviolet ray passed through a polarization filter.Thus, a polymer having anisotropy in refractive index in a directionperpendicular to the liquid crystal layer (i.e., in a directionperpendicular to the substrate) was formed in this manner.

[0175] Because the constitution of this Example comprises fabricatingthe drive circuit and the pixel portion TFT on a single substrate, thefabrication cost can be minimized.

EXAMPLE 3

[0176] The present Example explains in detail the constitution of aliquid crystal electro-optical device with reference to FIGS. 7(A) and7(B). An active matrix circuit consisting of a thin film transistor 500and a common electrode 403 is formed on a substrate 401. Theconstitution of the active matrix circuit is shown in FIG. 10.

[0177] In FIGS. 7(A) and 7(B), single pixel is defined by the effectivearea of an electric field formed between the electrodes 402 provided onboth side planes of a support 405 constituting a wall, and theelectrodes 403 provided on two supports 405.

[0178] The drain electrodes 402 were formed on both side planes of thewall 405 made from an insulating material. The drain electrode wasinsulated per pixel. Furthermore, a polyimide resin was used as theinsulating material constituting the wall.

[0179] Referring to FIG. 7(A), an island-like silicon film 508 isprovided on a glass substrate 401 having thereon an undercoat film (notshown in the figure), and an aluminum gate line 501 is provided via agate insulating film 505 to form a thin film transistor 500.

[0180] A silicon nitride first interlayer insulating film 506 and asecond interlayer insulating film 507 made of a transparent polyimideresin were laminated on the above structure. A source line 502 is alsoshown in the figure.

[0181] A drain electrode line 503 was formed on the second interlayerinsulating film 507, and the electrode was connected to the drain regionof the thin film transistor 500 via a contact hole. A common line 504was provided on the second interlayer insulating film 507.

[0182] Furthermore, a polyimide resin wall 405 was provided on the uppersides of the thin film transistor and the common line 504.

[0183] Referring to FIG. 7(A), the wall 405 exhibits a rectangular crosssection. Otherwise, the wall may be provided as such having atrapezoidal cross section as is shown in FIG. 8(A).

[0184] Referring to FIGS. 7(A) and 8(A), drain electrodes 402 are formedon the side planes or slopes of the wall 405 over the thin filmtransistor 500, and common electrodes 403 are formed on the side planesor slopes of the wall 405 over the common electrode.

[0185] The drain electrode 402 is electrically connected with the drainelectrode line 503 in the lower region of the wall 405. Also, the commonelectrode 403 is electrically connected with the common line 504 in thelower region of the wall 405. The drain electrode and the commonelectrode in this case were formed from aluminum.

[0186] Each pixel was formed in this manner. That is, single pixel isformed by the two common electrodes of the above constitution and thedrain electrode interposed therebetween.

[0187] The common electrode 403 in this case is provided per pixel, at asize approximately the same as that of the opposing drain electrode.

EXAMPLE 4

[0188] The present Example refers to a process for fabricatingelectrodes on both side planes of a wall made of an insulating material.

[0189] Firstly, referring to FIG. 7(A), a silicon oxide film 2,000 Å inthickness was formed as an undercoat film on a Corning #1737 glasssubstrate 401 by means of thermal CVD.

[0190] Then, an amorphous silicon film was formed at a thickness of from300 to 2,000 Å, for instance, at a thickness of 500 Å by plasma CVD.

[0191] Thermal annealing at 600° C. or lower, preferably, at 550° C. orlower, was performed thereafter for crystallization. The crystallinitycan be further improved by performing annealing using a laser radiationor an intense light equivalent thereto after effecting thermalannealing.

[0192] In particular, a trace quantity of a catalyst element foraccelerating the crystallization of the amorphous silicon film, forexample, nickel, may be incorporated to increase the crystallinity andto thereby form a highly crystalline polysilicon film on an inexpensiveglass substrate. For details, reference may be made to JP-A-Hei 6-244103and the like.

[0193] An island-like silicon film 508 was obtained thereafter byetching the thus obtained silicon film. Then, a silicon oxide film wasformed by means of plasma CVD using TEOS at a thickness in a range offrom 500 to 1,200 Å, for example, 1,000 Å, to provide a gate insulatingfilm 505.

[0194] An aluminum film was then formed at a thickness of from 2,000 to6,000 Å by means of sputtering, and the resulting film was patterned toobtain a gate line 501.

[0195] Anodic oxide film from several hundreds to several thousands ofangstroms (Å) in thickness can be formed on the surface of the aluminumgate line 501 by applying anodic oxidation using a weakly acidicsolution as the chemical conversion solution. Thus, in the formation ofsource and drain regions of the thin film transistor, an offset regioncan be formed between the channel region and the source/drain regionafter implanting impurity ions by using the gate electrode as a mask.This offset region contributes to the lowering of OFF current in a thinfilm transistor. Furthermore, it prevents short circuit from formingbetween the wirings that are provided in a multilayer.

[0196] Impurity ions were then implanted by means of ion doping into theisland-like silicon regions in a self-aligned manner by using the gateline as a mask. Thus were obtained n-type or p-type imparted island-likesilicon regions.

[0197] It is effective to provide a peripheral drive circuit using apolysilicon thin film transistor on the outer side periphery of theactive matrix region, i.e., to establish a so-called monolithic typestructure. In this case, a complementary structure can be realized byproviding a p-channel type and an n-channel type thin film transistor.

[0198] A silicon nitride film was formed thereafter by means of plasmaCVD to provide a first interlayer insulating film 506 at a thickness ina range of from 3,000 to 6,000 Å, for instance, at a thickness of 4,000Å. This may be provided otherwise by using a silicon oxide film or amultilayered film of silicon oxide film and a silicon nitride film.

[0199] Then, a contact hole was formed by etching on the firstinterlayer insulating film provided on the source region of the thinfilm transistor. Then, an aluminum film, or a multilayered filmcomprising titanium and aluminum, was formed by means of sputtering andthe like to a thickness in a range of from 2,000 to 6,000 Å, forinstance, at a thickness of 3,000 Å, and the resulting film waspatterned to obtain a source line 502.

[0200] A polyimide or acrylic transparent organic resin film was formedon the resulting structure to provide a second interlayer insulatingfilm 507 at a thickness in a range of from 4,000 to 10,000 Å, forinstance, at a thickness of 5,000 Å. After forming a contact hole on thedrain region of the thin film transistor 500, a coating of anelectrically conductive material, for instance, a film of aluminum,copper, chromium, titanium, ITO, etc., was formed by means of a knownprocess such as sputtering, and the resulting coating was patterned toobtain a drain electrode line 503 and a common line 504.

[0201] After coating the entire surface of the substrate with aphotosensitive polyimide and prebaking it, the resulting polyimide filmwas patterned by means of photolithography. A polyimide wall 405 wasformed thereafter by applying post baking to the patterned polyimidefilm. Thus, referring to FIG. 7(A), a wall having an approximatelyrectangular cross section, about 2 μm in width and about 6 μm in height,was formed in this case.

[0202] Referring to FIG. 8(A), a wall 405 having a trapezoidal crosssection can be obtained by appropriately controlling the intensity ofthe ultraviolet ray and the mask pattern in sensitizing polyimide.Although not shown in the figure, furthermore, a wall cross sectionhaving a curved plane is also available.

[0203] If the cross section of the wall 405 is rectangular, there may becases in which an electrically conductive material does not sufficientlyadhere to the side planes in forming electrically conductive films inthe later process steps to provide drain electrodes and commonelectrodes. In such a case, there is fear of causing contact failure andthe like. Accordingly, in such a case, it is particularly preferred toform a wall 405 having a trapezoidal cross section.

[0204] Preferably, sufficient cleaning is performed around the bottomportion of the wall 405 so that polyimide is removed perfectly. Care isrequired in this case, because, if unnecessary polyimide should bepresent, the electric connection between the drain electrode and thecommon electrode, or that between the drain electrode line and thecommon line may become insufficient.

[0205] After forming an electrical conductor, which may be of the sametype as that of the common line 504 or the drain electrode line 503, orof the type different therefrom, for instance, after forming an aluminumthin film by a known methods such as sputtering, the thin film waspatterned to obtain a drain electrode 402 and a common electrode 403. Inthis manner, a drain electrode 402 and a common electrode 403 can beformed on the side planes of the wall 405.

[0206] Then, a sealing material (not shown in the figure) was formed byusing epoxy resin on the periphery of one of the substrates, and thesubstrates 400 and 401 were laminated to form a cell.

[0207] In the present example, the wall 405 can be used as a spacer sothat it may function to maintain the distance between the substrates. Insuch a case, the process step for providing the spacers can be omitted.As a matter of course, spacers may be further incorporated as in anordinary liquid crystal electro-optical device to maintain a constantdistance between the substrates.

[0208] The material constituting the liquid crystal layer was thenfilled between the substrates by means of vacuum injection and the likeand sealed.

[0209] In the present example, a solution comprising uniformly mixedprepolymer and a nematic liquid crystal was used as the liquid crystalmaterial. More specifically, an urethane acrylate based photocurableresin was used as the prepolymer (polymer material) in this case. Apolymerization initiator was added into the solution to initiate thecuring reaction.

[0210] Then, ultraviolet ray was irradiated over the entire substrate tocure (polymerize) the prepolymer between the substrates.

[0211] In the present case, a linearly polarized ultraviolet ray havinga predetermined polarization direction was irradiated by using apolarization filter to form a polymer having a molecular structure withorientation in a predetermined direction. In this manner, a polymerhaving anisotropy in refractive index can be obtained.

EXAMPLE 5

[0212] The present Example refers to a fabrication step in which acommon electrode 403 and a drain electrode 402 are constituted from awall-like electrically conductive material.

[0213] The electrodes above were fabricated by forming a film of anelectrically conductive material constituting the common electrode 403and the drain electrode 402, e.g., aluminum, according to a known meanssuch as sputtering, on a substrate having formed thereon a common line504 and a drain electrode line 503.

[0214] The film above were formed at a film thickness corresponding tothe height necessary for the common electrode 403 and the drainelectrode 402 that are formed in a wall-like structure; the film wasformed, for instance, at a thickness of 6 μm.

[0215] Then, known patterning process was performed after forming aphotoresist on a film made of an electrically conductive material.

[0216] A wall-like electrode was formed by anisotropic etching, forinstance, by applying plasma etching under applied bias voltage, andproceeding the etching in the direction perpendicular to the substrateplane. Wall-like common electrode 403 and drain electrode 402 wereformed in this manner. As is shown in FIG. 7(B), the wall-like commonelectrode 403 and drain electrode 402 has a rectangular cross section.

[0217] Otherwise, the cross section of the electrodes above may betrapezoidal. In such a case, isotropic plasma etching or wet etching isapplied after forming a photoresist. Otherwise, a combination ofisotropic etching and anisotropic etching may be performed.

[0218] In the present Example, the common electrode 403 and the drainelectrode 402 are formed by using the same material, but they may beformed by using different materials.

[0219] The same process steps as those described in Example 4 werefollowed to finally obtain a liquid crystal electro-optical device.

EXAMPLE 6

[0220] The present Example refers to a constitution in which areagradation display is implemented with reference to FIG. 9.

[0221] In the present constitution, four regions 600 to 603 in a 2×2matrix are used to display 5 gradations. In this case, aforementionedfour regions (hereinafter referred to as “blocks”) constitute one pixel.

[0222] The advantage of this method is that the image data can be inputin binary value “H” or “L”. Because image data can then be processed asdigital data, a DA (digital/analog) conversion circuit can be omitted.This signifies that a control circuit inclusive of a peripheral circuitcan be more easily fabricated on the glass or quartz substrate of theliquid crystal panel.

[0223]FIG. 10 shows a case in which an active matrix is formed based onthe constitution above. Referring to FIG. 10, a gate line (scan line)720 and a data line 701 are placed in a lattice-like arrangement.Furthermore, a common electrode (see FIGS. 7(A) and (B) as well as FIGS.8(A) and (B)) is extended perpendicular or approximately perpendicularfrom a common line 730 fixed at a predetermined potential. A pixelelectrode is placed corresponding to this common electrode, and isconnected individually to the drains of the thin film transistors 702,704, 706, and 708. Furthermore, the pixel electrode is extendedperpendicular or approximately perpendicular to the substrate via thepixel electrode line. The pixel electrode is placed in such a mannerthat the electrode plane thereof may be parallel or approximatelyparallel to the aforementioned common electrode.

[0224] The image signals a to d are taken into the data line 701according to the controlled timing of sampling signal 700 from ahorizontal scanning control circuit (H driver) 721, and are then takenin the sampling hold circuit 722 which retains the data for apredetermined duration of time.

[0225] The operation of the horizontal scanning control circuit issynchronized with the externally applied horizontal scanning standardclock HCLK, and the scanning in the horizontal direction is activated bya horizontal scanning start signal HSYNC.

[0226] By thus activating the sampling signal 700, the datacorresponding to image signals a to d are supplied to data lines 701(701 a, 701 b, 701 c, and 701 d).

[0227] Scanning in the vertical direction is controlled by a verticalcontrol circuit (V driver) 723. The operation of the vertical scanningcontrol circuit 723 is synchronized with the externally applied verticalscanning standard clock VCLK, and the scanning in the vertical directionis activated by a vertical scanning start signal VSYNC.

[0228] The scan line 720 is connected to the vertical scanning controlcircuit 723, and scans and controls two lines at the same time. The scanline provides the gate signal to each of the thin film transistors, andcontrols the ON and OFF of the connection between the source and thedrain of the corresponding transistor.

[0229] In this manner, the image signals are applied to the blocks viathe four data lines (two data lines per 4 lines) selected by thehorizontal control circuit on the two lines selected by the scan line ofthe vertical control circuit 723.

[0230] The data line 701 above is connected as signal lines 701 a, 701b, 701 c, and 701 d which independently apply image input levels to thesource of the four thin film transistors 702, 704, 706, and 708. Thus,the aforementioned four image input control the bright and dark statesof the liquid crystal layers 703, 705, 707, and 709 corresponding to thefour display blocks.

[0231] When the above process is repeated by the horizontal controlcircuit for all of the pixels in the horizontal direction, the verticalcontrol circuit activates the subsequent scan line to repeat the sameoperation corresponding to the maximum number of pixels. In this manner,a single image plane of a gray-scale image display is implemented.

[0232] FIGS. 9(A) to 9(E) show an example of displaying bright and darkgradation. A single pixel is constituted from four regions 600, 601,602, and 603. In case the aforementioned scan line is activated, fivedisplay states shown in FIGS. 9(A) to 9(E) are realized depending on theinput value of image signals a to d.

[0233] (A) All the image input are in “L” level, and all the blocks arein dark state. This is the darkest state when viewed as a single pixel.

[0234] (B) The image signal a alone is in “H” level, and the block 600is in bright state.

[0235] (C) The image signals a and b are in “H” level, and the blocks600 and 601 are in bright state.

[0236] (D) The image signals a, b, and c are in “H” level, and the allthe blocks except block 603 are in bright state.

[0237] (E) All the image input are in “H” level, and all the blocks arein bright state. This is the brightest state when viewed as a singlepixel.

[0238] Thus, the gradation is controlled by the area of bright and darkdisplay blocks.

EXAMPLE 7

[0239] The present example refers to a constitution which implements agradation display by a method other than that described above. Morespecifically, the present constitution comprises controlling the timeperiod of displaying bright and dark states in each pixel. That is, thetwo states, i.e., the bright and dark states, are changed during adisplay period (generally one frame) of a certain pixel.

[0240] For instance, in a certain pixel, a bright state is provided fora half of the display period, and a dark state is provided for the nexthalf of the display period. Because the change in bright and dark stateswithin a frame (generally {fraction (1/30)} second) cannot be visuallyrecognized, an observer perceives the display as if it displays theimage at a half the gradation realized by displaying a bright state forthe entire display period. A display with multiscale gradation ispossible by thus controlling the time period for displaying the brightand dark states.

[0241] To conduct the gradation display above, image data are displayedby utilizing the data input into the liquid crystal electro-opticaldevice after dividing a single frame into a plurality of frames.

[0242] However, a still higher speed drive must be implemented becausethe time for refreshing the frame becomes shorter with increasing numberof scales.

[0243] As described in the foregoing, the present invention provides abrighter active matrix type liquid crystal electro-optical device with ahigher contrast, yet having a wider visual angle.

What is claimed is:
 1. A liquid crystal display device comprising: afirst substrate; a second substrate opposed to the first substrate witha gap therebetween; at least one common electrode and at least one pixelelectrode formed over the first substrate; and a liquid crystal layerbetween the first substrate and the second substrate, wherein at leastone of the common electrode and the pixel electrode has a wall-likeshape and an effective plane in a direction perpendicular to thesubstrate.
 2. A liquid crystal display device according to claim 1,wherein an electric field is applied in parallel with the substrate. 3.A liquid crystal display device according to claim 1, the device furthercomprising a thin film transistor over the first substrate, wherein thepixel electrode is connected to the thin film transistor.
 4. A liquidcrystal display device comprising: a first substrate; a secondsubstrate; a plurality of electrodes over the first substrate; and aliquid crystal layer between the first substrate and the secondsubstrate, wherein each of the plurality of electrodes has an effectiveplane in a direction perpendicular to the substrate, and wherein theplurality of electrodes are arranged in rows and effective planes of theplurality of electrodes in adjacent rows are arranged in parallel witheach other.
 5. A liquid crystal display device according to claim 4,wherein an electric field is applied in parallel with the substrate. 6.A liquid crystal display device according to claim 4, the device furthercomprising a thin film transistor over the first substrate, wherein thepixel electrode is connected to the thin film transistor.
 7. A liquidcrystal display device according to claim 4, wherein the plurality ofelectrodes comprise a common electrode and a pixel electrode.
 8. Aliquid crystal display device comprising: a first substrate; a secondsubstrate opposed to the first substrate with a gap therebetween; atleast one common electrode and at least one pixel electrode formed overthe first substrate; and a liquid crystal layer between the firstsubstrate and the second substrate, wherein at least one of the commonelectrode and the pixel electrode has a wall-like shape and an effectiveplane in a direction perpendicular to the substrate, and wherein atleast one of the common electrode and the pixel electrode comprises aninsulating support constituting the wall and a conductive material on asurface of the support.
 9. A liquid crystal display device according toclaim 8, wherein an electric field is applied in parallel with thesubstrate.
 10. A liquid crystal display device according to claim 8, thedevice further comprising a thin film transistor over the firstsubstrate, wherein the pixel electrode is connected to the thin filmtransistor.
 11. A liquid crystal display device comprising: a firstsubstrate; a second substrate opposed to the first substrate with a gaptherebetween; at least one common electrode and at least one pixelelectrode formed over the first substrate; and a liquid crystal layerbetween the first substrate and the second substrate, wherein at leastone of the common electrode and the pixel electrode has a wall-likeshape and an effective plane in a direction perpendicular to thesubstrate, and wherein at least one of the common electrode and thepixel electrode has a cross section of trapezoidal shape.
 12. A liquidcrystal display device according to claim 11, wherein an electric fieldis applied in parallel with the substrate.
 13. A liquid crystal displaydevice according to claim 11, the device further comprising a thin filmtransistor over the first substrate, wherein the pixel electrode isconnected to the thin film transistor.
 14. A liquid crystal displaydevice comprising: a first substrate; a second substrate opposed to thefirst substrate with a gap therebetween; at least one common electrodeand at least one pixel electrode formed over the first substrate; and aliquid crystal layer between the first substrate and the secondsubstrate, wherein at least one of the common electrode and the pixelelectrode has a wall-like shape and an effective plane in a directionperpendicular to the substrate, and wherein at least one of the commonelectrode and the pixel electrode has a cross section of curved plane onan edge portion thereof.
 15. A liquid crystal display device accordingto claim 14, wherein an electric field is applied in parallel with thesubstrate.
 16. A liquid crystal display device according to claim 14,the device further comprising a thin film transistor over the firstsubstrate, wherein the pixel electrode is connected to the thin filmtransistor.